Rotary screen coaters are known for applying a hot melt material, such as an adhesive, to a moving web, such as raw paper or label stock, passing by the coater. Typically, these rotary screen coaters include a die located within and fixed in position with respect to a rotating cylindrical screen. The die applies a supply of adhesive to an inner surface of the cylindrical screen and forces it through openings in the screen to the moving web. An impression roll provides a backing surface for the web as it is being coated. Examples of such devices include the apparatus shown in U.S. Pat. No. 5,213,033 to Bourgeois et al., and the Nordson rotary screen coater, manufactured by the assignee of the present invention.
Operational difficulties may be encountered with such rotary screen coaters if the die is not positioned properly with respect to the inner surface of the screen, or if the impression roll is not positioned properly with respect to the outer surface of the screen. In such cases, the adhesive may not be applied to the inner surface of the screen, or to the web, in a continuous, even, and homogeneous manner.
Further difficulties may be experienced if the screen is not evenly heated across its entire surface to insure the fluidity of the hot melt material. Typically, the ends of the screen cool quicker than the center of the screen. If the temperature at the ends of the screen is not maintained, adhesive at these end locations of the screen may sufficiently cool so as to clog the screen openings at these locations.
Moreover, downtime may be exaggerated if replacing the screen becomes difficult and time consuming. The screens in such devices require changing for replacement or maintenance, or if another type or size of screen is desired for a particular coating operation. Known rotary screen coaters often require substantial disassembly of the coater mechanics to access the screen.
Accordingly, it is an object of the present invention to provide a rotary coater device which facilitates removal of the screen for replacement or maintenance, which permits precise positioning of the die and the impression roll with respect to the inner and outer surfaces of the screen, and which assures an evenly heated outer screen surface.